Production of finely divided particles of synthetic polymers



United States Patent 3,334,070 PRODUCTION OF FINELY DIVIDED PARTICLES OF SYNTHETIC POLYMERS Jean Claude Chezaud, Saint Rambert llle Barbe, France,

assignor to Societe Rllodiaceta, Paris, France, a corporation of France No Drawing. Filed May 23, 1962, Ser. No. 196,903 Claims priority, application France, May 30, 1961,

863,326 4 Claims. (Cl. 260-75) This invention relates to the production of fine particles of synthetic polymers, and to the products obtained.

The mechanical strength properties of synthetic fibres, more especially those based upon polyamides, polyesters and the like, have led to the use of these fibres, in constantly increasing proportions, in very varied industrial felds. These fields include notably the paper industry, the techniques of which may also be employed in the production of other non-woven fibrous structures.

Synthetic fibres may be added to the usual cellulose pulps in order to increase the strength of the papers obtained. Papers of entirely synthetic nature have also been made, but in this case it is necessary to use bonding agents of varying kinds to ensure cohesion of the fibres. For this purpose there have been proposed more especially solutions of mineral salts, dispersions of fusible synthetic resins, in particular of N-alkoxy-alkyl polyamides, and thermoplastic fibres which melt or soften at temperatures at which the base fibres undergo no deterioration. The cohesion of the fibres in the paper has been ensured during calendering, which was effected in the first case at a temperature at which the mineral salt solutions swell and locally plasticise the synthetic fibres, thus ensuring their mutual adhesion, and in the other two cases at a temperature above the melting or softening point of the bonding agent.

There has recently been described a process for producing fibrous and/or foliated (leaf-like) structures which may be employed either alone or in mixture with synthetic fibres and, if desired, natural fibres, for the production of paper. This process consists in subjecting a polymer, in the incompletely solidified or coagulated state, to an intense shearing and/0r beating action, which in the case of soluble polymers may take place at the time when they are precipitated from their solution, said shearing and/or beating action being regarded as essential for producing structures capable of bonding.

It has now been found that it is possible to obtain finely divided particles of synthetic linear polymers which can be used as binders in papers without any mechanical shearing or beating action.

The process of the invention comprises incorporating in a gel of a synthetic linear polymer a solid compound which is soluble in an aqueous medium, so as to obtain an intimate mixture of consistency between that of a pulp and that of a powder, dispersing the mixture in an aqueous medium which dissolves or solubilises the incorporated solid compound, and separating the fine particles thus formed from the liquid.

The term gel is employed in the normal way to denote solid or semi-solid two-phase systems in which the two phases are continuous. In the case of polyamide gels in particular, their appearance ranges from that of hard products having a waxy appearance and handle with the maximum polymer content, to that of products which become increasingly rubbery in proportion as the solvent content increases.

It could not have been supposed that it would be possible by such a simple process to obtain sufficiently finely divided particles possessing high water-retaining power (they readily absorb up to twenty times their weight of 3,334,070 Patented Aug. 1, 1967 water), because it has heretofore been considered that only techniques employing an intense shearing and/or beating action could give a structure suitable for the object envisaged.

The solid compound may be added to a solution of the polymer, which is thereafter allowed to gel. This procedure gives a particularly homogeneous mixture.

The solid compounds employed may advantageously be mineral salts such as sodium chloride or sodium sulphate. The choice of a particular salt is generally a question of cost. The salt may be recovered, if necessary, by evaporation of the mother liquor after separation of the precipitated particles. It may be desirable, in order to favour the formation of very fine particles, to use a carbonate as the compound to be added to the polymer gel, and then to disperse the mixture in acidified water. The brisk effervescence produced by the evolution of carbon dioxide facilitates the bursting of the polymer particles.

Instead of a salt, a water-soluble organic colloid may be used, for example gelatine, carboxymethylcellulosc, an alginate, etc. Mixtures of the required consistency are obtained when the polymer gel is mixed with at least an equal weight of such a salt or of a gel of such a watersoluble colloid.

As the linear polymer to be obtained in powder form it is often advantageous to use an interpolymer which is soluble in solvents which are more readily accessible than are most solvents for the corresponding homopolymers. There may be mentioned more especially the interpolyamides, for example the binary copolymers derived from hexamethylene diammonium adipate and caprolactam and the ternary copolymers derived from these two compounds and hexamethylene diammonium sebacate, and interpolyesters, for example interpolyesters derived from terephthalic acid, ethylene glycol and tetra methylene glycol, or from ethylene glycol and terephthalic and isophthalic acids (or sebacic or hexahydroterephthalic acid, etc.).

The polymer gels which are treated preferably contain from 10% to 50% of polymer. The necessary quantity of soluble salt or colloid in relation to the amount of the gel varies with the nature of the polymer and with the nature of the added salt. It must be sufficient for the mixture of the salt or colloid with the polymer gel to possess a consistency between that of a pulp and that of a powder.

The particles precipitated and separated from the mother liquor containing the soluble salt or colloid in solution may be used as such after washing and straining, or may first be dried under moderate conditions which do not cause any substantial modification of their physical structure. They can readily be re-dispersed in water, for example in aqueous suspensions of synthetic or other fibres intended for the production of paper, non-woven fibrous sheets, etc. These products can be made by forming a felt, e.g. a paper, from the suspension in the known way, i.e. by deposition on a wire or the like followed by drying, and subsequently heating it at least to the melting temperature of the particles, so causing them to bond the fibres together. Naturally, the felt should not be heated to a temperature at which either the fibres or the bonding particles decompose. I

The following examples illustrate the invention. Per centages are by weight.

Example I 10 g. of an aqueous alcoholic gel containing 28% of an interpolyamide derived from 60% of hexamethylene diammonium adipate and 40% of caprolactam is introduced into a motar. There are slowly added to this gel, with crushing by means of a pestle, g. of sodium chloride capable of passing through a screen having a mesh size of 0.149 mm. There is finally obtained a very finely divided powder which is dry to the touch and which does not stick to the walls of the mortar or to the pestle.

This powder is thrown into 500 cc. of water at 13 C., whereupon it forms extremely tenuous flakes. These flakes, whose dimensions are between and 60 have considerable water-retaining power; they retain about 25 times their weight of water after straining. They are rinsed with one litre of Water at 13 C. Until completely free from the salt.

(a) Into a disintegrator containing 2 litres of water and rotating at 2000 r.p.m. are introduced 10 g. of these strained flakes (representing 0.4 g. of interpolyamide) with 1.6 g. of polyhexamethylene adipamide fibre having a count of 1.5 denier and a staple length of 4 mm. The proportion of these flakes employed as bonding agent is therefore 20% calculated on their mixture with the fibre.

When the dispersion is homogeneous, it is introduced onto a laboratory mould having a 100 mesh (U.S.A. system) screen, i.e. a mesh aperture of 0.149 mm. The sheet obtained, when suction-dried on a Buchner filter and then removed, possesses good wet strength similar to that of sheets obtained from mechanical pulps which have undergone a small degree of beating. It is dried for 30 seconds between a plate heated at 180 C. and a felt, and then subjected for 40 seconds to a pressure of 25 kg./cm. between two chromium-plated plates polished and coated with silicones, and heated at 180 C. The melting of the bonding agent binds the fibres together. There is obtained after cooling a sheet having a weight of 98 g./m. and possessing the following characteristics:

Tearing index: 571 (this index is obtained by dividing by the weight of the paper, in g./m. the value given in kg. by the Lhome and Argy ED 1 apparatus).

Bursting index: 30.5 (this index is obtained by dividing by the weight of the paper, in g./m. the value given in g./cm. by the Miillen paper tester).

Breaking length in m.:4220.

(b) In the same apparatus are mixed 20 g. of the same flakes (representing 0.8 g. of interpolyamide) and 1.2 g. of polyhexamethylene adipamide fibre having a count of 1.5 denier and a length of 4 mm., giving a proportion of bonding agent in the sheet of about 40%.

This mixture is introduced onto a laboratory mould under the same conditions as under (a). The sheet obtained possesses the following characteristics:

Tearing index 293 Bursting index 63 Breaking length 5140 Example II There are introduced into a mortar 8 g. of an aqueous alcoholic gel containing 41% of an interpolyamide obtained from:

There are slowly added 64 g. of sodium chloride passing through a screen having a mesh aperture of 0.149 mm, the gel meanwhile being crushed with the pestle. As the salt is added, the gel becomes converted into a very finely divided powder which is dry to the touch. By sprinkling the powder into 500 cc. of water at 13 C., there are obtained very fine flakes Whose dimensions are in the neighbourhood of 50111.. After straining, they possess a water retaining power of 25 times their dry weight. They are rinsed until completely free from salt.

(a) Into a disintegrator containing 2 litres of water and rotating at 2000 r.p.m. are introduced 10 g. of the rinsed and strained flakes (representing 0.4 g. of interpolyamide) and 1.6 g, of polyhexamethylene adipamide fibres having a count of 1.5 denier and a length of 4 mm. The proportion of flakes employed as bonding agent is thus 20% of the whole mixture. When the dispersion is homogeneous, it is introduced onto a laboratory mould provided with a detachable mesh screen (0.149 mm. aperture).

The sheet obtained, when suction-dried on a Buchner filter and then removed, possesses good wet strength. It is dried for 30 seconds between a plate heated at 150 C. and a felt. It is then pressed for 40 seconds under 25 kg./cm. between two chromium-plated, polished and silicone-coated plates at a temperature of C. The melting of the bonding agent binds the fibres together. There is obtained on cooling a sheet having a weight of 99 g./m. and possessing the following characteristics:

Tearing index 490 Bursting index 33.5 Breaking length 3473 Tearing index 410 Bursting index 64.3 Breaking length 3473 Example III I By a procedure similar to that of Examples I and II, 10 g. of an aqueous alcoholic gel containing 18% of an interpolyamide identical with that of Example I are mixed with 10 g. of a gelatine gel containing 30% of dry substance. Two gels are crushed together so as to produce a pulp. This pulp, when thrown into water at 40 0., forms spongy interpolyamide fragments which can readily be reduced into minute flakes.

Sheets are prepared by the method of Example I, mixing with these flakes polyhexamethylene adipamide fibres having a count of 1.5 denier and a length of 4 mm.

The characteristics of the sheets obtained are very similar to those indicated in Example I.

Example IV In a colour grinder having a capacity of 2 litres are mixed 20 g. of calcium carbonate of coarse grain size and 10 g. of an aqueous alcoholic gel containing 10% by weight of an interpolyamide identical to that of Example II. A homogeneous pulp is obtained, which is poured into a litre vat filled with water acidified with 10% of hydrochloric acid. As a result of the action of the acid on the calcium carbonate, carbon dioxide is evolved, which divides the interpolyamide into a multitude of very spongy flakes possessing a high water retaining power.

These flakes, when strained and rinsed, can readily be redispersed, for example in the presence of polyamide fibres.

Sheets are prepared by the procedure of Example II from polyhexamethylene adipamide fibres having a count of 1.5 denier and a length of 4 mm., and the flakes of this example have characteristics very similar to those of the sheets of Example II.

Example V 75 her, in which it gels.

The pulp obtained is fractionated with a spatula so as to divide the coarser fragments, and it is then thrown into water at 20 C. By solution of the salt in the water flakes are formed, which are separated from the mother liquor and then washed with pure water.

These flakes possess a high water retaining power (at least times their weight) and can readily be re-dispersed, for example in the presence of polyamide fibres.

Sheets are prepared with them and by the method of Example II, with polyhexamethylene adipamide fibres having a count of 1.5 denier and a length of 4 mm., so that the sheet obtained contains as bonding agent 0% of the flakes.

These sheets, when pressed under the conditions described under (a) in Example II, have characteristics very similar to those indicated in that example.

Example VI By a procedure similar to that of Examples I and II, 80 g. of sodium chloride passing through a screen having a mesh aperture of 0.149 mm. are mixed with 10 g. of a gel containing, in methylene chloride, about 210% of an interpolyester derived from ethylene glycol and a mixture of hexahydroterephthalic acid and terephthalic acid, in molecular proportions of 25/75.

A finely divided powder is obtained, which is thrown into 500 cc. of water at ambient temperature. Very fine flakes are obtained, Whose dimensions are of the order of 50 1. When strained, they possess a Water retaining power of about times their weight. They are rinsed until completely free from salt.

Sheets are prepared by the method of Example I, mixing with these flakes polyethylene terephthalate fibres having a count of 1.5 denier and a length of 4 mm., so that the proportion of flakes employed as bonding agent is of the total weight of their mixture with the fibre.

After drying and pressing under conditions identical to those of Example I, except that the pressing temperature is 155 C., a sheet is obtained which has a weight of 79.8 g./m. and which possesses the following characteristics:

Tearing index 480 Bursting index 30 Breaking length 1200 Example VII 6 acid and terephthalic acid in molecular proportions of 33/67.

A powder is obtained, which is poured into a 1 litre vat filled with water acidified with 10% of hydrochloric acid, as in Example IV.

The flakes obtained, when strained and rinsed, can readily be re-dispersed in water, for example in the presence of polyethylene terephthalate fibres.

Sheets are prepared from these flakes in the manner indicated in Example VI, the pressing temperature being 180 C. The sheets obtained possess characteristics similar to those mentioned in that example.

I claim:

1. Process for the production of finely divided particles of linear synthetic thermoplastic polymers by forming an intimate mixture of a polymer selected from the group which consists of linear polyamides and linear polyesters and a solid substance which is inert towards the said polymer, which comprses forming a gel of the said polymer, producing therefrom an intimate mixture of the said gel and of a solid substance selected from the group which consists of sodium chloride, and sodium sulphate, the ratio by weight of the said solid substance to the polymer gel being at least 1:1, dispersing the mixture so obtained in an aqueous medium in which the said solid substance forms a solution, and separating from the aqueous medium the fine particles of polymer so formed.

2. Process according to claim 1, wherein the said solid substance is sodium chloride.

3. Process according to claim 1, wherein the said solid substance is sodium sulphate.

4. Process according to claim 1, wherein the said aqueous medium contains hydrochloric acid.

References Cited UNITED STATES PATENTS 2,544,483 3/1951 Baum 260-2.5

2,795,008 6/1957 Lindemann et al. 2602.5

2,822,350 2/1958 Hayes 260- 3,062,760 11/1962 Dermody et al. 260-25 3,203,911 8/1965 Goullioud 260-78 FOREIGN PATENTS 1,199,550 6/1959 France.

WILLIAM H. SHORT, Primary Examiner.

M. WOLES, SAMUEL H. BLECH, S. L. BASHORE,

R. LYON, Assistant Examiners. 

1. PROCESS FOR THE PRODUCTION OF FINELY DIVIDED PARTICLES OF LINEAR SYNTHETIC THERMOPLASTIC POLYMERS BY FORMING AN INTIMATE MIXTURE OF A POLYMER SELECTED FROM THE GROUP WHICH CONSISTS OF LINEAR POLYAMIDES AND LINEAR POLYSTERS AND A SOLID SUBSTANCE WHICH IS INERT TOWARDS THE SAID POLYMER, WHICH COMPRISES FORMING A GEL OF THE SAID POLYMER, PRODUCING THEREFROM AN INTIMATE MIXTURE OF THE SAID GEL AND OF A SOLID SUBSTANCE SELECTED FROM THE GROUP WHICH CONSISTS OF SODIUM CHLORIDE, AND SODIUM SULPHATE, THE RATIO BY WEIGHT OF THE SAID SOLID SUBSTANCE TO THE POLYMER GEL BEING AT LEAST 1:1, DISPERSING THE MIXTURE SO OBTAINED IN AN AQUEOUS MEDIUM IN WHICH THE SAID SOLID SUBSTANCE FORMS A SOLUTION, AND SEPARATING FROM THE AQUEOUS MEDIUM THE FINE PARTICLES OF POLYMER SO FORMED. 